During the manufacturing of LEDs with vertical contacts, the LEDs are typically first formed on a growth substrate and subsequently bonded to a carrier via copper-copper (Cu—Cu) or nickel-tin (Ni—Sn) bonding. FIGS. 1A-1C illustrate a process for manufacturing an LED with Ni—Sn bonding in accordance with the prior art. As shown in FIG. 1A, the process initially includes forming N-type gallium nitride (GaN) 14, GaN/indium gallium nitride (InGaN) multiple quantum wells (“MQWs”) 16, and P-type GaN 18 on a substrate material 12 with a buffer material 13. Subsequently, a first metal stack 19 is formed on the P-type GaN 18 via sputtering, electrolysis, and/or other suitable techniques. The first metal stack 19 includes a barrier material 20 (e.g., tungsten/titanium (W/Ti)), a copper (Cu) seed material 22, nickel (Ni) 24, and tin (Sn) 26.
As shown in FIG. 1B, a similar second metal stack 19′ is formed on a carrier 32. The second metal stack 19′ includes a barrier material 20′, a copper (Cu) seed material 22′, nickel (Ni) 24′, and tin (Sn) 26′. The multiple materials of the first and second metal stacks 19 and 19′ are selected based on a target stress level on the substrate material 12. As shown in FIG. 1C, the substrate material 12 with the first metal stack 19 is then stacked on the carrier 32 such that the first and second metal stacks 19 and 19′ face each other. The first and second metal stacks 19 and 19′ are then bonded to each other using an annealing process to form an assembly 10. The substrate material 12 (shown in phantom lines) is then removed from the assembly 10 before the assembly 10 is diced into individual LED dies.
The bonded substrate material 12 and the carrier 32 formed according to the process discussed above tend to bow and/or otherwise flex with temperature fluctuations. Such flexure can crack and/or otherwise damage the N-type GaN 14, the GaN/InGaN MQWs 16, and/or the P-type GaN 18. Also, it has been observed that various materials in the first and/or second metal stacks 19 and 19′ tend to peel off from the assembly 10 during dicing. It is believed that delamination between two adjacent materials in the first and second metal stacks 19 and 19′ contribute to such delamination. In addition, the foregoing assembling process is time consuming and costly because a large number of metals are deposited in series. Accordingly, several improvements to the bonding techniques used to efficiently manufacture LED dies may be desirable.